Cards holding electronic components in an electronic computer are many times cooled by driving air over the cards to be cooled. Many times, printed circuit boards are designed such that a variable number of cards to be cooled may by attached thereto. The air volume that passes over the cards to be cooled may vary significantly depending on the number of cards installed. If there is a small number of cards installed, the resistance to air traveling over the cards is reduced, which may allow a larger volume of air to pass, reducing air volume over other areas which need to be cooled, thus unbalancing the air cooling system such that some elements may not receive the air needed to sufficiently cool them.
U.S. Pat. No. 4,399,485 issued Aug. 16, 1983 to Wright et al. for AIR BAFFLE ASSEMBLY FOR ELECTRONIC CIRCUIT MOUNTING FRAME discloses a variable width baffle assembly which may be folded between two spaced apart circuit boards to maintain a constant, uniform impedance to the flow of cooling air across a vacant space on a partially populated electronic mounting frame for printed circuit board assemblies.
U.S. Pat. No. 4,730,233 issued Mar. 8, 1988 to Osterman for ARRANGEMENT IN COOLING CIRCUIT BOARDS discloses a arrangement for cooling circuit boards which are accommodated in magazines. Each magazine is assigned a regulator plate having a plurality of through holes the sizes and position of which are selected such that air flow may be adjusted to the cooling needs of the board being cooled.